The following description of the background of the invention is provided simply as an aid in understanding the invention and is not admitted to describe or constitute prior art to the invention.
Cystic fibrosis (CF) is the most common severe autosomal recessive genetic disorder in the Caucasian population. It affects approximately 1 in 2,500 live births in North America (Boat et al., The Metabolic Basis of Inherited Disease, 6th ed., pp 2649-2680, McGraw Hill, N.Y. (1989)). Approximately 1 in 25 persons of northern European Caucasian descent are carriers of the disease. The responsible gene has been localized to a 250,000 base pair genomic sequence present on the long arm of chromosome 7. This sequence encodes a membrane-associated protein called the “cystic fibrosis transmembrane regulator” (or “CFTR”). The CFTR genomic DNA is well characterized and known in the art. See, for example, Anand et al. (Genomics 9: 124-130, 1991), U.S. Pat. No. 5,939,255 to Anand et al., and the online Cystic Fibrosis Mutation Database (initiated by the Cystic Fibrosis Genetic Analysis Consortium in 1989), all of which are incorporated herein by reference. There are greater than 1000 different mutations in the CFTR gene, each having varying frequencies of occurrence in different populations, presently reported to the Cystic Fibrosis Genetic Analysis Consortium. These mutations exist in both the coding regions (e.g., ΔF508, a mutation found on about 70% of CF alleles, represents a deletion of a phenylalanine at residue 508) and the non-coding regions (e.g., the 5T, 7T, and 9T variants correspond to a sequence of 5, 7, or 9 thymidine bases located at the splice branch/acceptor site of intron 8) of the CFTR gene.
The major symptoms of cystic fibrosis include chronic pulmonary disease, pancreatic exocrine insufficiency, and elevated sweat electrolyte levels. The symptoms are consistent with cystic fibrosis being an exocrine disorder. Although recent advances have been made in the analysis of ion transport across the apical membrane of the epithelium of CF patient cells, it is not clear that the abnormal regulation of chloride channels represents the primary defect in the disease.
A variety of CFTR gene mutations are known. The identification of additional mutations will further assist in the diagnosis of cystic fibrosis.